Advancement in integrated circuit technology has lead to increased numbers of electronic circuits being located in very close proximity to each other within a system. Radio frequency interference (RFI) results when output voltages rise and fall quickly in response to voltage inputs. Radio frequency interference in an electronic circuit may negatively impact the proper operation of adjacent electronic circuitry. Consequently, as increased numbers of electronic circuits are located in very close proximity to each other, the negative consequences of RFI are multiplied.
For example, a light emitting diode (LED) lamp driver circuit may use a duty cycle controller to dim a brightness level of the lamp, such that the lamp is repeatedly switched on for only a specified percentage of an incremental time unit. The incremental time unit may be very small, resulting in the lamp voltage being repeatedly switched at a high frequency in order to properly execute the duty cycle over several time units and to thereby dim the lamp. Such high frequency switching in the lamp driver circuit may cause undesired RFI which negatively impacts the proper operation of adjacent electronic circuitry. In this example, RFI may be reduced by controlling the rise and fall times of voltages output by the lamp driver circuit in response to the repeatedly switched voltage inputs provided by the duty cycle controller.
Previous approaches have utilized digital circuitry to slow the rise and fall times of output voltages. However, these digital approaches typically fail to slow the output voltage response as extensively as desired for various applications. Other approaches incorporate analog circuitry to slow the rise and fall times of an output voltage. However, typical analog approaches incorporate a capacitor having high capacitance for monitoring the rate of output voltage response. The large amount of integrated circuit area occupied by such a high capacitance capacitor is undesirable in various applications. Moreover, many previous approaches produce inconsistent rise and fall times that significantly vary according to temperature and fabrication conditions.
Therefore, a need has arisen for a method and circuitry for controlling voltage in an electronic circuit, such that radio frequency interference is reduced, such that integrated circuit area is minimized, and such that consistent rise and fall times are produced despite variations in temperature and fabrication conditions.